Blade systems have become very popular due in part to their high density of computing, control and/or storage capacity, the variety of the blade modules which can be accommodated and the ease with which blade modules may be installed or replaced. For example, the BladeCenter® system from IBM® has a chassis with power supplies, cooling and fourteen slots for various combinations of blade devices, including servers, hard drives and RAID and other storage controllers. Additionally, the chassis includes bays into which fibre channel (FC) and serial attached SCSI (SAS) switches may be installed. Each slot and switch bay includes connectors for both FC and SAS blade devices. Similarly, the switch includes both FC and SAS interconnections. The FC and SAS slot and switch connectors are typically provided in redundant pairs but for clarity will be referred to and illustrated herein as single connectors.
In one blade implementation (FIG. 1), a blade enclosure 100 houses one or more FC and/or SAS switches 102 and a number of server blades 104. External storage 106 in the form of “just a bunch of disks” (JBOD) or a “switched bunch of disks” (SBOD) in a storage area network (SAN) is connected to the switch 102 through a pair of external redundant RAID controllers 108A, 108B. For greater efficiency and convenience, a more recent blade implantation (FIG. 2) includes the entire SAN within a blade enclosure 200 on one chassis: FC and SAS switches 202, server blades 204A, 204B, disk drive blades 206A, 206B, and dual (redundant) RAID controller blades 208A, 208B.
Each blade slot is comprised of one port for each FC and SAS connector. Each FC port consists of a single physical layer (“PHY”) while each SAS port can be defined to be (or have associated with it) one or more PHYs, such as 4, 8 or 16. A PHY is the portion of a network device in which data is encoded (or decoded) and transmitted (or received) to another device on the network. Multi-PHY ports are designed for the increased bandwidth and speed of newer, “wider” SAS fabrics and some newer blades require more than one slot. However, current switches (also known as expanders), which support 14 slots, have 12, 24 or 36 PHYS. A 36-PHY switch can thus accommodate only 36/4=9 4-PHY (4X) blades. Put another way, 14 4X blades require 56 SAS PHYS and would need to be handled by three 36 PHY switches for full any-to-any connectivity, two switches, each using seven ports (28 PHYS) for blades and the remaining ports (8 PHYs) with which to connect to a third switch for multiplexing. Such a complicated configuration runs counter to the desire to reduce the number of components as well as reduce cost, power and space requirements. Moreover, it is expected that future BladeCenters will implement more and wider fabrics (that is, greater than 4X) thereby exacerbating the problem.
Consequently, a need remains for a fully contained blade system with wide fabrics and multi-slot blades but which can be implemented with a single SAS 36-PHY switch.